Coated abrasive articles generally contain an abrasive material, typically in the form of abrasive grains, bonded to a backing by means of one or more adhesive layers. Such articles usually take the form of sheets, discs, belts, bands, and the like, which can be adapted to be mounted on pulleys, wheels, or drums. Abrasive articles can be used for sanding, grinding, or polishing various surfaces of, for example, steel and other metals, wood, wood-like laminates, plastic, fiberglass, leather, or ceramics.
The backings used in coated abrasive articles are typically made of paper, polymeric materials, cloth, nonwoven materials, vulcanized fiber, or combinations of these materials. Many of these materials provide unacceptable backings for certain applications because they are not of sufficient strength, flexibility, or impact resistance. Some of these materials age unacceptably rapidly. Also, some are sensitive to liquids that are used as coolants and cutting fluids. As a result, early failure and poor functioning can occur in certain applications.
In a typical manufacturing process, a coated abrasive article is made in a continuous web form and then converted into a desired construction, such as a sheet, disc, belt, or the like. One of the most useful constructions of a coated abrasive article is an endless coated abrasive belt, i.e., a continuous loop of coated abrasive material. In order to form such an endless belt, the web form is typically cut into an elongate strip of a desired width and length. The ends of the elongate strip are then joined together to create a "joint" or a "splice."
Two types of splices are common in endless abrasive belts. These are the "lap" splice and the "butt" splice. For the lap splice, the ends of the elongate strip are bevelled such that the top surface with the abrasive coating and the bottom surface of the backing fit together without a significant change in the overall thickness of the belt. This is typically done by removing abrasive grains from the abrasive surface of the strip at one of the ends, and by removing part of the material from the backing of the elongate strip at the other end. The bevelled ends are then overlapped and joined adhesively. For the butt splice, the bottom surface of the backing at each end of the elongate strip is coated with an adhesive and overlaid with a strong, thin, tear-resistant, splicing media. Although endless coated abrasive belts containing a splice in the backing are widely used in industry today, these products suffer from some disadvantages which can be attributed to the splice.
For example, the splice is generally thicker than the rest of the coated abrasive belt, even though the methods of splicing generally used involve attempts to minimize this variation in the thickness along the length of the belt. This can lead to a region(s) on the workpiece with a "coarser" surface finish than the remainder of the workpiece, which is highly undesirable especially in high precision grinding applications. For example, wood with areas having a coarser surface finish will stain darker than the remainder of the wood.
Also, the splice can be the weakest area or link in the coated abrasive belt. In some instances, the splice will break prematurely before full utilization of the coated abrasive belt. Belts have therefore often been made with laminated liners or backings to give added strength and support. Such belts can be relatively expensive and under certain conditions can be subject to separation of the laminated layers.
In addition, abrading machines that utilize a coated abrasive belt can have difficulty properly tracking and aligning the belt because of the splice. Further, the splice creates a discontinuity in the coated abrasive belt. Also, the splice area can be undesirably more stiff than the remainder of the belt. Finally, the splice in the belt backing adds considerable expense in the manufacturing process of coated abrasive belts.